Male and female pandas were housed in enclosures with animals of the opposite sex on either side. They were allowed limited physical interaction with their neighbors through cage bars.

Scientists measured the animals' "mate preference behavior", which included different forms of playfulness and bond-forming, as well as sexual arousal.

Negative interactions could include signs of aggression or a mere lack of interest.

The animals were then introduced to each other for mating－with both preferred and non-preferred partners.

"The highest reproductive performance was seen when both males and females showed mutual preference," the researchers found.

The results should come as no big surprise. Ever since Charles Darwin published his theory of sexual selection in 1859, scientists have understood that mate selection is key to animal reproduction.

"Mate incompatibility can impede captive breeding programs by reducing reproductive rates," the study authors wrote. "It is therefore surprising that mate preferences have not figured more prominently in captive breeding programs."

"The future of conservation breeding will not take place in a test tube," they wrote.

Conservation group WWF estimates there are only about 1,600 pandas left in the wild in south-central China.